1. Field of the Invention
This invention relates to moisture curable organosiloxane compositions. More particularly this invention relates to additives for organosiloxane compositions that cure by the reaction of silanol-containing polyorganosiloxanes with organosilicon compounds containing silicon-bonded hydrolyzable groups. Preferred additives impart increased working time to the composition without any substantial reduction in cure rate.
2. Background Information
The prior art describes organosiloxane compositions that cure to yield crosslinked elastomers and other useful products in the presence of moisture by the reaction of polyorganosiloxanes containing at least two silanol groups per molecule with organosilicon compounds containing at least three silicon-bonded alkoxy or other hydrolyzable groups per molecule as the curing agent. This reaction is typically catalyzed by tin compounds or organotitanium compounds.
When the curing agent is an alkoxy silane and the curing catalyst is a tin compound the reactive ingredients of these compositions are typically packaged in two containers with the curing agent and curing catalyst in one container and the silanol-containing polyorganosiloxane in a second container. The curing reaction occurs when the contents of the two containers are combined in the presence of atmospheric moisture.
The time interval over which the composition can be fabricated by pouring, molding, extrusion, calendaring or other known shaping technique is referred to in the art as the "working time" of the composition.
The length of time over which the portion of the composition containing the silanol-terminated polyorganosiloxane can be stored without exhibiting a substantial increase in viscosity is referred to in the art as "storage stability".
For certain applications such as mold making it would be desirable to prepare relatively large batches of curable material containing all of the reactive ingredients, including the curing agent and curing catalyst, and have the material remain workable over a relatively long time period by delaying the initiation of the curing reaction without substantially decreasing the rate of this reaction once it begins.